The epithelial-mesenchymal transition (EMT) is a complex cell-biological program that operates during the progression of carcinoma cells to high-grade malignancy, conferring on these cells many of the attributes associated with aggressive tumors, including the ability to disseminate to distant sites and to seed metastatic colonies. This program is orchestrated by a series of pleiotropically acting master transcription factors (EMT- TFs) that organize the complex changes in gene expression causing the replacement of a large cohort of epithelial cell proteins with those associated with the mesenchymal cell state. A major, critical level of control required for expression of the aggressive mesenchymal state is poorly understood however: the precursors of many of the mRNAs whose expression changes during the EMT also undergo alternative splicing (AS) that confer on resulting mature, processed mRNAs altered properties, including changes in stability, protein-coding information, and responsiveness to microRNA-mediated inhibition. The current fragmentary insights into the effects of AS on the execution of the EMT program make it impossible to form a reasonably complete understanding of how this critical cell-biological program is effected. The proposed research will begin by enumerating the hundreds of AS events that occur in response to several alternative mechanisms of inducing an EMT program both in cultured cells and in a living tissue. Having done so, bioinformatics algorithms will be employed to determine the sequences adjacent to involved splice sites. Thereafter, using the known nucleotide-recognizing properties of the large array of already-characterized RNA- binding, splice-regulating proteins, predictions will be made by these algorithms about the identities of the splice-regulators that are likely to b responsible for the observed large-scale shifts in AS occurring during passage through an EMT. This experimental strategy should yield the identities of key regulators of AS that are likely to b as important functionally as the EMT-TFs in executing the EMT program. Experimental tests designed to functionally test the candidacies of these AS factors will be performed. These tests will gauge whether the forced or blocked expression of these factors affect execution of critical components of the EMT program, and whether, as predicted, such imposed changes in AS factor expression affect the production of key EMT-associated proteins, i.e., proteins that play key roles in the expression of the epithelial versus mesenchymal cell phenotypes observed during malignant progression. This work also has the potential to identify novel biomarkers of the EMT program that are applicable, for example, for the detections of stem cells in a variety of epithelial tissues.